1. Field of the Invention
This invention relates to an electro-mechanical energy conversion element (piezoelectric element) which is a vibration generating source and a vibration type driving device having at least a vibration member including the conversion element.
2. Related Background Art
Piezoelectric elements as electro-mechanical energy conversion elements are used for various purposes, and in recent years they have been used as vibration generating sources constituting vibration members in vibration wave driving devices, such as vibration wave motors. Such a piezoelectric element is used as the vibration generating source of a vibration member of a pencil type vibration wave motor in which the piezolectric element is sandwiched between cylindrical metal blocks and causes the flexural vibration of the metal blocks, whereby the metal blocks are moved relative to a contact member in contact with the metal blocks by the circular or elliptical motion of the surface particles of the metal blocks caused by the flexural vibration, or as the vibration generating source of a vibration member of a ring-like vibration wave motor in which the piezoelectric element is adhesively secured to one surface of a ring-like metallic resilient member and forms a travelling wave in the metallic elastic member, for example, by the combination of two standing waves and relatively moves a contact member in contact with this elastic member.
For example, the piezoelectric element may be used in a pencil type vibration wave motor, as described in Japanese Patent Application Laid-Open No. 3-40767 or Japanese Patent Application Laid-Open No. 3-117384, which is a structure including a plurality of circular piezoelectric elements. The polarizing direction of the elements in the direction of thickness alternates so that elements to the left and right or before and behind a particular element have an opposite polarizing direction. Electrode films are formed on both surfaces of each piezoelectric ceramic plate and are positionally provided with a phase difference of 90.degree. and are superposed one upon another while being sandwiched between electrode plates.
FIG. 8 of the accompanying drawings shows the front surface of a disc-shaped piezoelectric element used as the vibrator of a pencil type vibration wave motor. This piezoelectric element is made by molding ceramic powder having a piezoelectric property using a press method or an extrusion method, and thereafter sintering it to form piezoelectric ceramics, working the piezoelectric ceramics into a circular shape having a predetermined thickness, and thereafter forming thereon an electrode film by a vapor deposition method or a printing method. The electrode film A1 and electrode film B1 on the front surface are divided by a gap GS (hereinafter referred to as the slit) of a predetermined width in the diametrical direction, and the back surface (not shown) is generally formed with electrode film.
The portions of the piezoelectric ceramics in the areas corresponding to the electrode film A1 and electrode film B1 are polarized in different polarizing directions (+) and (-).
Now, when the vibration member of such a pencil type vibration wave motor is to be assembled, it is necessary to assemble it while recognizing the orientation/direction of the element associated with the polarizing direction of the above-described piezoelectric element, and various marks for such recognition have been proposed.
As shown, for example, in FIG. 9 of the accompanying drawings, a plurality of cut-aways C are formed in the outer peripheral portion of the piezoelectric element by machining or the like to thereby provide a mark, or as described in Japanese Patent Application Laid-Open No. 4-306888, the widths a1 and a2 of slits GS.sub.1 and GS.sub.2 dividing the electrode film A1 and electrode film B1 on the front surface as shown in FIG. 10 of the accompanying drawings are changed to e.g. a1&gt;a2, whereby the orientation/direction of the element associated with the polarizing direction of the piezoelectric element can be correctly recognized.
Also, recently, a stacked piezoelectric element comprising a plurality of piezoelectric elements made integral with one another and sintered has been made, and a reduction in the driving voltage of the vibration wave motor and the downsizing of such motor have been attempted.
Such a stacked piezoelectric element 1, as shown in FIG. 6 of the accompanying drawings, is made by the internal electrodes 6 of a plurality of elements 1 which are indicated by hatching being connected together by inter-layer wiring 4 formed in the interior of the elements. The reference numeral 3 designates surface via-hole electrodes formed in the surface of the stacked piezoelectric element 1.
Such inter-layer wiring 4 in the interior of the elements is called a via-hole (through-hole) electrode, and can be made by a manufacturing technique for low-temperature sintered ceramics circuit substrates.
Generally, the stacked piezoelectric element 1 can be made by forming a hole in a green sheet of piezoelectric ceramics, filling the hole with conductor paste, printing an electrode pattern as internal electrodes on the surface of the green sheet by the use of the conductive paste, and thereafter stacking a plurality of such green sheets to form a stacked-sheet member, and sintering it. As a result of the stacked piezoelectric element having been made in this manner, the internal electrodes 6 and the via-hole electrode (inter-layer wiring) 4 become integral with each other, and the wiring for connecting the layers of the element together can be formed.
The stacked piezoelectric element made in this manner, when used in a pencil type vibration wave motor, is held by and between metal blocks D1 and D2, as shown in FIG. 7 of the accompanying drawings, and at the same time, a wiring substrate E is brought into pressure contact with that surface of the stacked piezoelectric element 1 which has the surface via-hole electrodes 3 to thereby make electrical contact (conduction) possible, and the element is fastened and fixed by a bolt BLT.
An electrical conductor layer on the wiring substrate E conducts to each surface via-hole electrode 3 on the surface of the stacked piezoelectric element 1, whereby there is formed an electrically conducting pattern capable of supplying electric power to the piezoelectric element 1.
In the construction of the vibration member F as described above, the surfaces of the stacked piezoelectric element 1 must be smooth and parallel. If element 1, after sintered, has deformation or distortion caused therein, it is necessary to work the upper and lower surfaces of the element to thereby make these surfaces smooth.
Therefore, to recognize the orientation/direction of the stacked piezoelectric element 1 when the vibration member of a vibration type driving device such as a vibration wave motor using the stacked piezoelectric element 1 is assembled, it is known to form cut-aways in the outer peripheral portion of the element (as in the aforedescribed piezoelectric element, which is a single plate) or to attach additional electrode film or the like after the surface working to thereby provide a mark.
However, the formation of the cut-aways takes much time and labor and adds a post-manufacturing step which leads to an increase in cost, and it has been found that the cut-away portions adversely affect the vibration of the vibration member.
Also, after the surface working, the direction of the element cannot be accurately determined, and there arises a case where no mark can be provided.